Abstract: Use of Hydrogeology, Geochemistry, and Geothermometer Models in Reconnaissance Exploration for a Hydrogeothermal Resource

Richard Howard Pearl, James K. Barrett

Several hydrogeothermal-resource exploration methods can delineate favorable sites within large geographic areas. An exploration problem has been to find a hydrogeothermal deposit in the United States that can be used to generate electricity. Such a deposit would need to have a large amount of readily available groundwater, whose temperature is in excess of 200°C, contained in a highly permeable reservoir.

On a worldwide basis, hydrogeothermal deposits generally are located in areas of recent tectonism, relatively young acidic volcanic rocks, and high heat flow. Such conditions are present in the western United States, including the mountainous areas of Colorado. Geologic and heat-flow maps of Colorado show that optimum conditions for a hydrogeothermal reservoir exist primarily along the Rio Grande rift zone and in the San Juan Mountains of southwestern Colorado.

Further definition for the hydrogeothermal resource potential of Colorado is the presence of about 150 thermal springs and wells (surface-water temperatures in excess of 21°C). Although these springs and wells are located throughout the western half of Colorado, most of them are in the southwestern quarter of the state and along the Rio Grande rift zone.

A final reconnaissance delineation, using geothermometer models such as SiO₂, Na-K, Na-K-Ca, and mixing, reveals several thermal areas in Colorado where predicted subsurface temperatures exceed 200°C. Further exploration efforts should be undertaken to determine the size and extent of these hydrogeothermal reservoirs as well as the groundwater availability and permeability of the subsurface formations at each site.

AAPG Search and Discovery Article #90969©1977 AAPG-SEPM Rocky Mountain Sections Meeting, Denver, Colorado